Multivibrator frequency divider chain for musical instrument employing a master oscillator which is step frequency adjustable and a twin-t vibrato oscillator



Jan. 20, `197'0 D. VOLPE 3,490,327

MULTIVIBRATOR FREQUNCY DIVIDERCHAIN FOR MUSICAL INSTRUMENT EMPLOYING AMASTER OSCILLATOR WHICH IS STEP FREQUENCY ADJUSTABLE AND A TWIN-TVIBRATO OSCILLATOR Iqnclus E Vope.

llaM

-BY Diaz/w WQ www ATTORNEYS Jan. 20, 1970 D. VOLPE 3,490,327

MULTIVIBRATOR FREQUENCY DIVIDER CHAIN FOR MUSICAL INSTRUMENT EMPLOYING AMASTER OSCILLATOR WHICH Is STEP FREQUENCY ADJUSTABLE AND A TWIN-TVIBRATO OSCILLATOR Filed Aug. 26, 1966 V 2 Sheets-Sheet s QUDIO OUTPUT5l GNQL l i- INVENTOR K IqDo-xus D. Vdpe BY mi@ Mq www ATTORNEYS UnitedStates Patent O U.S. Cl. 84-1.25 5 Claims ABSTRACT OF THE DISCLOSUREThis disclosure relates to a tone producing system wherein a lirstoscillator provides a manually selectively variable frequency. Theoscillator is Iarranged to have its signal phase shifted at `apredetermined frequency to provide a vibrato effect. The outputfrequency of the oscill-ator is further divided to provide musical tonesover a wide frequency range.

This invention relates generally to musical instruments and moreparticularly to a device for lproviding musical accompaniment for amusical instrument.

In the past there have been disclosed -various electronic devices -forproviding 'an electronic generated sound to accompany the playing of amusical instrument. The prior art shows these electronic devices asbeing controlled by the keys of an instrument, such as an accordian. Thecontrol keys have been arranged to set the frequency of the soundproduced by the electronic device, so as to provide an accompaniment forthe melody played on the instrument itself. In order to simulate thevibrato eifect of an instrument, there has also been incorporated in theprior art devices means for amplitude modulating the electronic signalprovided.

Although such systems have been available for many years, they have notobtained wide acceptance because of the electronic type of soundproduced bythe device. Furthermore, the prior art devices were quitelimited in the frequency range which they could provide, due primarilyto the manner in Iwhich the electronic sound was generated.

Therefore, to overcome the disadvantages of the prior art as well as toprovide an electronic device which emits a sound closely simulating thetonal qualities of the musical instrument itself, applicant hasinventedk -a new and improved device.

Accordingly, it is an object of this invention to provide a new andimproved device for generating a sound to accompany the playing of amusical instrument.

Another object of the invention is to provide a new and improved devicesimulating the sound of a musical instrument.

A further object of the invention is to provide la new and improveddevice for simulating the vibrato elfect produced while a musicalinstrument is played.

An additional object of the invention is to provide a new land improvedelectronic de-vice for providing music over a wide Ifrequency range toaccompany the playing of an instrument.

A further object of the invention is to provide an electronic devicewhich is capable of providing tonal accompaniment simultaneously in twoor more different frequency ranges.

Still other objects and advantages of the invention will in part beobvious and will in part appear from the speciication.

The invention accordingly comprises the -features of construction,combinations of elements and arrangements ICC of parts which will beexemplified in the constructions hereinafter set forth and the scope ofthe invention will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention,refe-rence is had to the following detailed description taken inconjunction with the accompanying drawings, in which FIG. 1 is a blockdiagram of the device according to the invention; and

FIG. 2. is a schematic diagram illustrating the circuitry forimplementing the device according to the invention.

Referring to FIG. 1, there is shown in block diagram form a device forproviding an electronic sound to accompany the playing of a musicalinstrument. At 10 there is shown an oscillator, such as a square waveoscillator, for producing `a square wave signal yat a frequency f1. Thissignal at the frequency f1 is then transmitted through a buffer stage 20to avoid loading or interaction of the subsequent circuitry with theoscillator 10. The signal 4from the buffer stage 20 isthen fed into afirst binary divider 21 where the fundamental frequency f1 is divided bya figure of 2 to provide a signal at a frequency f2. The frequency f2 isthen fed -from the binary divider 211 to the binary divider 22 wherebythe frequency f2 is divided by two, resulting in a frequency of f4 whichis onequarter of the fundamental frequency of f1. The signal f4 issubsequently divided by a third binary divider 23 to provide a signal off8 which is one-eighth of the fundamental frequency of f1.

By means of switches Sa-Sd shown at 24, any of the four harmonics orcombinations of the -four harmonics may be selected. It is to beunderstood that additional binary divider stages may also beincorporated to produce a greater number of different frequency signals.If desired, the harmonics fl-fs may be separately selected by a rotaryswitch Se shown at 25. These signals, noted as the audio-output signals,are then transmitted through a filter amplifier 26 to a loudspeaker 27.

In order to select the frequency at which the fundamental frequencyoscillator E10 is oper-ated, there is pro- |vided a key selector 30which could be mounted on la musical instrument such as an accordion,piano, etc., Ifor controlling the plurality of resistors 311-34 whichare coupled in circuit with the square wave oscillator |10. Bydepressing the various keys shown at '1 4 in the form of cont-acts whichare actuated by depressing the keys of the instrument, such .as anaccordion, certain ones of the resistors or combinations of theresistors 31-34, may be selected to vary the oscillation frequency ofthe square wave oscillator 10. A key arrangement of this type is shownin a patent to Martin 2,563,477 issued Aug 7, 1951.

In order to provide the vibrato effect, that is, a quivering effectencountered when listening to a wind instrument, there is provided avibrato oscillator which produces a sine wave frequency signal at afrequency much less than the frequency of oscillation of the square waveoscillator 10. This modulating signal is applied to the square waveoscillator 10, such that a phase shifting of the oscillator signal iscaused to occur at the same rate as the frequency of the signal providedfrom the vibrato oscillator 35.

In order to implement the block diagram of FIG. 1, reference should nowbe had to FIG. 2 wherein there is shown in schematic form the circuitryaccording to the invention. The various blocks shown in FIG. 1 are alsoshown in FIG. 2, wherein corresponding numbers, i.e. 10, 20-23, 30 and35, refer to the same device shown in block form in FIG. 1.

The square wave oscillator 10 is constructed in the form of a modifiedRC time constant multivibrator and comprises two NPN transistors 40 and41 having emitters 40a and 41a, collectors40b and 41b, and. bases 40eand 41e-, respectively. The emitters 40a and 41a are connected togetherthrough an emitter resistor 42 to ground. The collector 40h is connectedtoavoltage source +V and the collector 41b is connected through a loadresistor 44 to the same voltage source +V. In order to provide thepositive feedback signals to sustain oscillations, the collector 41b isconnected through a capacitor 45 to the base 40e of transistor 40. Asshown in FIG. 2, there are provided resistors 31-34 which arekey-actuated by the key selector 30 mounted on the musical instrument.The resistors 31-34 are coupled to base 40C of transistor 40 and areconnected through keys 1-4 to the base 41c through a resistor 46. To setthe voltage bias level at the base of transistor 41, there is provided avoltage divider network comprising resistors 47a `and 47b. There is alsoprovided a by-pass capacitor 48 coupled in parallel with resistor 47b.The output wave form from the square wave oscillator is shown at 49 andis coupled through a coupling capacitor 49a to the buffer stage 20. Therate of oscillation of oscillator 10 is established by the RC constantwhich is determined by the value of capacitor 45 and the resistance ofthe selected resistors 31,34 respectively.

The buffer stage 20 comprises an NPN transistor 50 having an emitter50a, a collector 50h and a base 50c. The lvoltage at base 50c is set bythe voltage divider network, comprising resistors 52 and 53respectively. The emitter 50a is grounded and the collector 50b isconnected to a load resistor 51 to a source of positive voltage +V. Thestage 20 operates as a buffer amplifier to avoid loading or interactionof the subsequent circuitry with the oscillator 10.

The output signal from the buffer stage 20 is then fed into the firstbinary divider stage 21. The irst binary divider stage 21 is thencoupled to a second binary divider stage 22 which again divides thesignal provided from the buffer stage 20. The last-mentioned dividerstage 22 is then coupled to a third divider stage 23 which also operateson the signal provided from the buffer 20 to again divide it by two.

Thus the frequency f1 is successively divided down by an integer which,in this case, is selected as two. It is to be understood that otherdivider Values may be selected without departing from the spirit andscope of this invention. Inasmuch as the binary dividers aresubstantially identical in form, they will all be describedsimultaneously.

The binary dividers 21-23 are in the form of triggered multi-vibrators.They are responsive to the signals provided from the buffer stage 20.The signals from buffer stage 20 are provided to the rst binary dividerstage 2'1 through an input capacitor 55 which is in turn shunted by acapacitor 56. The dividers 21-23 comprise transistors 60 and 61 havingemitters 60a and 61a, collectors 60b and 61b, and bases 60e` and 61C,respectively. Coupled between the collector 60b and the base 61C areresistor 63 and capacitor 64 which form a commutating network. There isalso coupled to collector 61b and base 60C of transistor 60, anothercommutating network shown comprising a capacitor 65 and a resistor 66.The collectors 60b and 61b are coupled through trigger and loadresistors 67 and 68 respectively which are, in turn, coupled through aresistors 69 to the voltage source. A high frequ'ency bypass capacitor70 is provided across the voltage source +V, as shown.

A description of a bi-stable multi-vibrator as utilized herein, may befound by reference to the text Pulse and Digital Circuits, Millman andTaub, (1956) published by McGraw Hill, and yin particular, Chapter 5 ofsaid text.

The binary dividers are coupled together such that they form a chain toprovide signals at a frequency of f2 which is equal to f1 divided bytwo, f4 which is equal to f1 divided by four, and f8 which is equal tof1 divided by eight. These signals may then be combined by theutilization of switches 24 and 25 to provide a combination of, orindividual ones of, these signals. In this manner, over three andone-half octaves of tonal accompaniment may be provided. v

As mentioned previously, although the dividing chain utilized hereinprovides division to the base two, division may be accomplished to adilferent base. For example, in Chapter 11 of the aforementioned textPulse and Digital Circuits, there is shown a sixteen binary dividerchain modified by feedback techniques to provide a scale of ten binarydivider chain. It is therefore to be understood that this invention isnot specifically limited to the use of the base two as the dividerinteger.

As previously disclosed, in order to provide a vibrato eifect such as tosimulate the playing of a wind instrument, there ,is shown a vibratooscillator 35 which comprises an NPN transistor having an emitter 80a, acollector 80b and a base 80C. The emitter 80a is grounded and thecollector 80b and base 80e are connected together through twinT-networks comprising resistors 81 and 82, capacitor 83, capacitors 84and 85, and resistors 86 and 87. These are coupled together to form atwin T phaseshift oscillator which, by virtue of the resistances 81 and82, capacitors 84 and 85, are made to oscillate at a slow sine wavefrequency such as, for example, between 6-18 cycles per second. Thissignal is then applied to the base 41e of transistor 41 of oscillator 10to phase-shift the output signal provided from the oscillator 10. Themodulating signal provided from oscillator 35 will cause the transistor41 of oscillator 10 to turn on at different times, depending upon thefrequency of oscillation of the vibrato stage 35. The vibrato signal isprovided through a switch 90 which, in turn, is coupled to a resistor 91and through a second switch 92. In this manner, the amplitude of thevibrato signal may be controlled.

While it will be understood that the circuit specifications may varyaccording to the design for any particular application, the followingcircuit specifications are included for the circuitry of FIG. 2, by wayof example only.

All transistors NPN No. MM-2151-2 Motorola.

Resistor 31 Pot. ohms-- 150 Resistor 32 ohms 15 Resistor 33 do 17Resistor 34 do 18 Resistor 44 do 2.2K Capacitor 45 microfarad-- .1Resistor 46 ohms-- 4.7K Resistors 47a, 47b do 3.3K Capacitor 48microfarads-- 5 Capacitor 49a do .05 Resistor 52 ohms 120K Resistor 53do 10K Resistor 51 do 4.7K Capacitors 55, 56 microfarad-- .002 Resistors63, 66 ohms-- 22K Capacitors 64, 65 microfarad-- .002 Resistors 67, 68ohms 4.7K Resistor 69; binary divider 21 do 6.8K Resistor 69; binarydivider 22 do. 4.7K Resistor 69; binary divider 23 do 2.2K Resistors 81,82 do 220K Capacitor 83 microfarad-- .7 Capacitors 84, 85 do .5 Resistor86 ohms-- 150 Resistor 87 Pot. ohms..- 3000 Resistor 91 ohms-- 330K Infrequency f1 of oscillator 10 c.p.s 1396.8

It will thus be seen that the objects set forth above, among those madeapparent from the preceding description, are eiiiciently obtained andsince certain changes may be made in the above constructions withoutdeparting from the spirit and scope of the invention, it is intendedthat all matter contained in the above description or shown in theaccompanying drawings shall be interpreted as illustrative and not in alimiting sense.

It is also to be understood that the following claims are intended tocover all of the generic and specific features of the invention hereindescribed and all statements of the scope of the invention which, as amatter of language, might be said to fall therebetween.

What is claimed is:

1. In a musical instrument, an oscillator for providing a first signalat a frequency f1, said oscillator cornprising a free-runningmultivibrator having a resistancecapacitance circuit which determinesthe frequency f1, divider means responsive to said first signal fordividing said frequency by a number to provide a second signal at afrequency f2, and a control unit responsive to the play ing of saidinstrument to control said oscillator in order to set the rst signal ata predetermined frequency, said control unit comprising a plurality ofresistance elements adapted to be selectively placed in saidresistance-capacitance circuit of said multivibrator, said firstoscillator comprising first and second amplifying units each havinginput terminals, said control unit coupled between the input terminalsof said amplifying units, and a second oscillator having an outputterminal providing a vibrato phase shift signal, said second oscillatorhaving its output terminal coupled to the input terminal of said secondamplifying unit.

2. An electronic musical instrument, including a first oscillator, saidfirst oscillator comprising first and second amplifying units eachhaving input and output terminals, energy storage means connectedbetween said input terminals of said first unit to the output terminalof said second unit, a control unit comprising a plurality of resistancemeans and a plurality of key means for selecting said resistance means,said control unit coupled between said input terminal of said first unitand said input terminal of said second unit, and a second oscillatorproviding a vibrato frequency shift signal, said second oscillatorcoupled to said input terminal of said second unit.

3. An instrument in accordance with claim 2, wherein said control unitcomprises a plurality of series-coupled resistors and a plurality of keymeans coupled at one end with each other, said key means coupled attheir other ends `to said resistors at a point between different ones ofsaid resistors.

4. An instrument in accordance with claim 3, wherein said amplifyingunits are transistors and wherein said input terminals are baseelectrodes and said output terminals collector electrodes.

5. An instrument in accordance with claim 2, wherein said secondoscillator comprises a twin T phase shift oscillator. l

References Cited UNITED STATES PATENTS 2,128,367 8/1938 Kock 84--1.252,563,477 8/1851 Martin 331-144 2,598,790 6/ 1952 Harrison 331-1443,286,197 11/1966 Borsattino et al. 331-113 2,545,469 3/1951 Jordan331--48 3,283,057 11/1966 Campbell 84-1.01 3,358,068 12/ 1967 Campbell84-1.01

OTHER REFERENCES Electronic Musical Instrument Handbook, Crowhurst(April 1962).

HERMAN KARL SAALBACH, Primary Examiner F. PRINCE BUTLER, AssistantExaminer

